Optical system for detecting motion of a body

Abstract

The invention relates to a system ( 1 ) for detecting motion of a body ( 2 ), said body comprising a first diffraction pattern ( 3 A) and a second diffraction pattern ( 3 B) with a predetermined orientation relative to said first diffraction pattern. The system comprises optical means ( 4 A, 4 B) adapted to provide at least a first incident beam to said first diffraction pattern to obtain a first diffracted beam from said first diffraction pattern and at least a second incident beam, with a predetermined orientation relative to said first incident beam, to said second diffraction pattern to obtain a second diffracted beam from said second diffraction pattern. The system has means for detecting motion of said body on the basis of the phase difference between at least one of said first diffracted beam and said second diffracted beam. Accordingly a larger in-plane rotation range is obtained for detecting motion of the body ( 2 ). The invention also relates to a wafer ( 2 ) provided with two-dimensional diffraction patterns ( 3 A, 3 B) and a method for detecting motion of a body.

1 . A system ( 1 ) for detecting motion of a body ( 2 ), said body comprising a first diffraction pattern ( 3 A) and a second diffraction pattern ( 3 B) with a predetermined orientation relative to said first diffraction pattern, wherein said system comprises:
 optical means ( 4 A,  4 B) adapted to provide at least a first incident beam ( 5 ) to said first diffraction pattern to obtain a first diffracted beam ( 6 ) from said first diffraction pattern and at least a second incident beam ( 7 ), with a predetermined orientation relative to said first incident beam, to said second diffraction pattern to obtain a second diffracted beam ( 8 ) from said second diffraction pattern;   means for detecting motion of said body on the basis of at least one of said first diffracted beam and said second diffracted beam.   
   
   
       2 . The system ( 1 ) according to  claim 1 , wherein at least one of said first diffraction pattern ( 3 A) and said second diffraction pattern ( 3 B) is a two-dimensional diffraction pattern. 
   
   
       3 . The system ( 1 ) according to  claim 1 , wherein said first diffraction pattern ( 3 A) is provided over said second diffraction grating ( 3 B). 
   
   
       4 . The system ( 1 ) according to  claim 1 , wherein said first diffraction pattern ( 3 A) determines a first plane and said second diffraction pattern ( 3 B) determines a second plane and wherein said first plane and second plane make an angle (α) with respect to each other. 
   
   
       5 . The system ( 1 ) according to  claim 1 , wherein said first diffraction pattern ( 3 A) and said second diffraction pattern ( 3 B) comprise a rectangular diffraction pattern and a radial diffraction pattern. 
   
   
       6 . The system ( 1 ) according to  claim 1 , wherein said first diffraction pattern ( 3 A) and said second diffraction pattern ( 3 B) are rectangular diffraction patterns rotated relatively to each other. 
   
   
       7 . The system ( 1 ) according to  claim 1 , wherein at least one of said first diffraction pattern ( 3 A) and said second diffraction pattern ( 3 B) comprises lines of varying widths adapted to provide absolute position information for said body. 
   
   
       8 . The system ( 1 ) according to  claim 1 , wherein said body further comprises marks adapted for visual inspection of the absolute position of said body. 
   
   
       9 . The system ( 1 ) according to  claim 1 , wherein said optical means comprise a first optical measurement system ( 4 A) and a second optical measurement system ( 4 B), wherein said first optical measurement system and/or said first diffraction grating ( 3 A) is adapted to allow selection of said first diffraction pattern by said first incident beam ( 5 ) and wherein said second optical measurement system ( 4 B) and/or said second diffraction grating ( 3 B) is adapted to allow selection of said second diffraction pattern by said second incident beam ( 7 ). 
   
   
       10 . The system ( 1 ) according to  claim 9 , wherein said first optical measurement system ( 4 A) and said second optical measurement system ( 4 B) are arranged with respect to each other such that motion of said body ( 2 ) within a specific range is either detected on the basis of said first diffracted beam ( 6 ) or said second diffracted beam ( 8 ). 
   
   
       11 . The system ( 1 ) according to  claim 1 , wherein said means ( 4 A,  4 B) for detecting motion of said body are adapted to measure a phase difference between at least one of said first incident beam ( 5 ) and said first diffracted beam ( 6 ) or said second incident beam ( 7 ) and said second diffracted beam ( 8 ). 
   
   
       12 . The system ( 1 ) according to  claim 1 , wherein said optical means comprises:
 means ( 4 A; 4 B) for providing a first, second and third incident light beam ( 51 , 71 ; 52 , 72 ; 53 , 73 ) to said first and/or second diffraction pattern ( 3 A, 3 B) from a first, second and third direction to obtain a first, second and third diffracted beam ( 61 , 81 ; 62 , 82 ; 63 , 83 );   means ( 4 A, 4 B) for measuring a phase difference between at least one of the pairs ( 51 , 61 ; 52 , 62 ; 53 , 63 ; 71 , 81 ; 72 , 82 ;  73 , 83 ) consisting of said first incident beam and said first diffracted beam, said second incident beam and said second diffracted beam and said third incident beam and said third diffracted beam to detect motion of said body ( 2 ).   
   
   
       13 . The system ( 1 ) according to  claim 11 , wherein said system comprises position sensitive detectors ( 10 ) arranged to receive further orders (0, −1) of said diffracted light beams ( 61 , 62 , 63 ; 81 , 82 , 83 ) to detect rotation of said body ( 2 ). 
   
   
       14 . A semiconductor wafer ( 2 ) with a first two-dimensional diffraction pattern ( 3 A) and a second two-dimensional diffraction pattern ( 3 B) arranged over said first diffraction pattern adapted to detect motion of said wafer ( 2 ). 
   
   
       15 . The wafer ( 2 ) according to  claim 14 , wherein said first diffraction pattern ( 3 A) and said second diffraction pattern ( 3 B) comprise a rectangular diffraction pattern and a radial diffraction pattern. 
   
   
       16 . The wafer ( 2 ) according to  claim 14 , wherein said first diffraction pattern ( 3 A) and said second diffraction pattern ( 3 B) are rectangular diffraction patterns rotated relatively to each other. 
   
   
       17 . A method for detecting motion of a body ( 2 ), said body comprising a first diffraction pattern ( 3 A) and a second diffraction pattern ( 3 B) with a predetermined orientation relative to said first diffraction pattern, wherein said method comprises the steps of:
 providing a first incident beam ( 5 ) to said first diffraction pattern to obtain a first diffracted beam ( 6 );   providing a second incident beam ( 7 ) to said second diffraction pattern to obtain a second diffracted beam ( 8 ), and   detecting motion of said body on the basis of at least one of said first diffracted beam and said second diffracted beam.   
   
   
       18 . The method according to  claim 17 , further comprising the steps of providing said first incident beam ( 5 ) to select said first diffraction pattern ( 3 A) and providing said second incident beam ( 7 ) to select said second diffraction pattern ( 3 B). 
   
   
       19 . The method according to  claim 17 , wherein said motion of said body ( 2 ) is detected by measuring a phase difference between at least one of said first incident beam ( 5 ) and said first diffracted beam ( 6 ) or said second incident beam ( 7 ) and said second diffracted beam ( 8 ). 
   
   
       20 . The method according to  claim 17 , wherein said method comprises the steps of:
 providing a first, second and third incident light beam ( 51 , 71 ; 52 , 72 ; 53 , 73 ) to said first and/or second diffraction pattern ( 3 A, 3 B) from a first, second and third direction to obtain a first, second and third diffracted beam ( 61 , 81 ; 62 , 82 ; 63 , 83 ), and   measuring a phase difference between at least one of the pairs ( 51 , 61 ; 52 , 62 ; 53 , 63 ; 71 , 81 ; 72 , 82 ;  73 , 83 ) consisting of said first incident beam and said first diffracted beam, said second incident beam and said second diffracted beam and said third incident beam and said third diffracted beam.   
   
   
       21 . The method according to  claim 17 , wherein said method further comprises the step of detecting rotation (R x ;R y ;R z ) of said body ( 2 ) by receiving further orders (0,−1) of said diffracted beams at position sensitive detectors ( 10 ).